The present invention relates generally to gas turbine engines, and, more specifically, to compressors thereof.
A turbofan gas turbine engine includes a fan followed in turn by a multi-stage axial compressor each including a row of circumferentially spaced apart rotor blades, typically cooperating with stator vanes. The blades operate at rotational speeds which can result in subsonic through supersonic flow of the air, with corresponding shock therefrom. Shock introduces pressure losses and reduces efficiency.
Fan blades are the largest form of compressor blades whose radially outer tips experience the greatest relative velocity and are subject to strong passage and leading edge shock waves.
A stationary casing surrounds the rotor blades and includes a radially inwardly facing inner surface defining a shroud which forms a small radial tip clearance or gap with the rotor blades during operation. As the blades compress or pump airflow between the flow passages defined between adjacent blades, a differential pressure is created between the opposite pressure and suction sides of each blade. This differential pressure causes a portion of the pressurized air to flow through the tip gap and reduces pumping efficiency.
Furthermore, the airflow leaking over the blade tips typically rolls up into a vortex near the casing shroud which generates significant efficiency loss and aerodynamic flow blockage.
The flow pumping capacity of a compressor rotor stage is its ability to maximize airflow through the passages between adjacent blades. Pumping should be effected with maximum efficiency, and with a suitable stall or throttle margin. Airfoil leakage at the blade tips creates an aerodynamic flow blockage in those outer portions of the flow passages between adjacent tips which decreases pumping capacity and efficiency.
The presence of shock waves at the blade tips increases this problem. As the tip vortex passes through a shock wave, rapid diffusion of the air occurs with corresponding pressure losses and increase in aerodynamic flow blockage.
Accordingly, it is desired to provide an improved compressor casing and cooperating blade tips for reducing tip vortex related performance loss and flow blockage for improving pumping efficiency and throttle margin.
A compressor casing includes an axially convex inner surface for surrounding a row of rotor blades with radial gaps therebetween. The tip of the blades complement the casing contour for reducing blade tip losses and flow blockage.